Thyristor element with short turn-off time and method for producing such element

Abstract

A fast switching thyristor having a shorted emitter structure in which, in order to shorten the turn-off time, the charge carrier lifetime is set to be low by means of recombination centers. The charge carrier lifetime in at least the control base zone of the thyristor is set initially to be homogeneous and low corresponding to a desired firing resistance underneath the emitter zone with respect to the voltage rise of the returning forward voltage in the thyristor after every recovery process, and the charge carrier lifetime is set to be low compared to the homogeneous setting in the partial region of the control base zone extending from below the control electrode substantially to the portion of the edge of the emitter zone which faces the control electrode but without contacting the edge of the emitter zone. If the thyristor is of the amplifying gate type having a shorted auxiliary emitter structure, then the charge carrier lifetime in the region between the main and auxiliary emitter zones is less than the charge carrier lifetime in the region between the auxiliary emitter zone and control electrode which in turn is less than the homogeneously set charge carrier lifetime in the bulk or volume of the device. Additionally, the density of the shorting channels in the edge region of the auxiliary emitter zone facing the control electrode is greater than in the remainder of this zone and than in the main emitter zone.

What is claimed is: 
     
       1. In a fast switching thyristor in which, in order to shorten the turn-off time, the charge carrier lifetime is set to be low by means of recombination centers, said thyristor including a semiconductor wafer having four zones of alternating opposite conductivity type including a control base zone which extends to one major surface of said wafer and an emitter zone which is formed within said control base zone adjacent said one major surface and which is penetrated by shorting channels emanating from said control base zone, an emitter electrode on said one major surface contacting said shorted emitter zone, and a control electrode on said one major surface contacting said control base zone; and wherein the charge carrier lifetime in said control base zone of said thyristor is set to be homogeneous and low corresponding to a desired firing resistance underneath said emitter zone with respect to the voltage rise of the returning forward voltage in said thyristor after every recovery process; the improvement wherein: the charge carrier lifetime is set to be lower compared to said homogeneous setting in the partial region of said control base zone extending from below the edge of said control electrode substantially to the portion of the edge of said emitter zone which faces said control electrode but without contacting said edge of said emitter zone. 
     
     
       2. In a fast switching thyristor of the amplified gate type in which, in order to shorten the turn-off time, the charge carrier lifetime is set to be low by means of recombination centers, said thyristor including a semiconductor wafer having at least four zones of alternating opposite conductivity type including a control base zone which extends to one major surface of said wafer and main emitter and auxiliary emitter zones which are formed within said control base zone adjacent said one major surface and which are penetrated by shorting channels emanating from said control base zone, a main emitter electrode and an auxiliary emitter electrode on said one major surface contacting said shorted main emitter zone and said shorted auxiliary emitter zone, respectively, and a control electrode on said one major surface contacting said control base zone; and wherein the charge carrier lifetime in said control base zone of said thyristor is set to be homogeneous and low corresponding to a desired firing resistance underneath said emitter zones with respect to the voltage rise of the returning forward voltage in said thyristor after recovery process; the improvement wherein: the charge carrier lifetime is set to be lower compared to said homogeneous setting in a first partial region of said control base zone extending from below the edge of said control electrodes substantially to the portion of the edge of said auxiliary emitter zone which faces said control electrode but without contacting said edge of said auxiliary emitter zone; the charge carrier lifetime is set to be even lower than in said first partial region in a second partial region of said control base zone extending from beneath the adjacent edge of the auxiliary emitter electrode substantially to the portion of the edge of said main emitter zone which faces said auxiliary emitter zone; and said shorting channels of said auxiliary emitter zone in the region thereof adjacent the edge of said auxiliary emitter zone which faces said control electrode are closer together than in the remaining region of said auxiliary emitter zone, and are closer together than said shorting channels in said main emitter zone. 
     
     
       3. A thyristor as defined in claim 1 wherein said partial region of said control base zone of said thyristor extends up to a distance of from 0.5 mm to 0.3 mm from said edge of said main emitter zone. 
     
     
       4. A thyristor as defined in claim 2 wherein said first and second partial regions of said control base zone of said thyristor extend up to a distance of from 0.05 mm to 0.3 mm from said edge of said auxiliary emitter zone and from said edge of said main emitter zone, respectively. 
     
     
       5. A thyristor as defined in claim 3 or claim 4 wherein said partial regions of said control base zones extend to 0.1 mm from said edge of the associated one of said emitter zones. 
     
     
       6. A thyristor as defined in claim 1 or claim 2 wherein said control electrode is centrally disposed on said one major surface of said semiconductor body.